1. Field of the Invention
The present invention relates to a wind turbine generator for generating electric power with a windmill which converts wind, which is a natural form of energy, into a rotational force.
This application is based on Japanese Patent Application No. 2004-381564, the content of which is incorporated herein by reference.
2. Description of Related Art
Wind turbine generators for generating electric power using wind power, which is a natural form of energy, are known. Such a wind turbine generator includes a nacelle disposed on a tower. The nacelle includes a rotor head equipped with blades, a main shaft connected to the rotor head so as to integrally rotate with the rotor head, a gearbox connected to the main shaft that rotates upon receiving the wind power supplied to the blades, and a generator driven by a shaft output from the gearbox. According to the wind turbine generator having this structure, the rotor head equipped with the blades, which convert wind power into a rotational force, and the main shaft rotate to generate a shaft output. The rotational speed is increased via the gearbox connected to the main shaft and the resulting shaft output is transmitted to the generator. Consequently, the shaft output obtained by converting the wind power into the rotational force is used as a driving source of the generator, and thus power generation can be performed using the wind power as motive power for the generator.
In the above-described known wind turbine generator, the rotor head is disposed at the front end of the nacelle, and the gearbox and the generator are placed on a nacelle bed provided behind the rotor head of the nacelle and in a casing forming the upper space of the nacelle bed (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-304094).
As described above, according to the structure of the known wind turbine generator, a rotational torque is transmitted from the rotor head provided at the front end of the nacelle to the main shaft, the rotational speed is increased with the gearbox, and the motive power is then transmitted to the generator for use. As a result, the drivetrain inevitably becomes long in the shaft direction. However, in the known structure, the gearbox and the generator, which are connected at the rear end of the main shaft, are placed in the casing provided behind the rotor head, and the inside of the rotor head is not used as a space for the drivetrain. Therefore, in order to obtain a space for placing the gearbox and the generator, the dimensions of the nacelle bed and the casing part of the nacelle must be increased particularly in the shaft direction, thereby increasing the size of the whole nacelle. Such an increase in the size of the nacelle increases the weight of the nacelle bed and the casing, resulting in an increase in weight of the nacelle itself.
Furthermore, since recent wind turbine generators tend to increase their output by increasing the size thereof, the sizes of components such as the rotor head, the main shaft, the gearbox, and the generator also increase, resulting in an increase in weight. In the same structure as that of the known wind turbine generator, in particular, since the overall structure of the nacelle, including the nacelle bed and the casing, further increases, it is inevitable that the weight of the whole nacelle drastically increases. The increase in weight of the nacelle has a significant undesirable effect on, for example, the design strength of the tower and production costs because the nacelle is a structure provided on the upper part of the tower. From this standpoint, it is desirable that the dimension of nacelle in the shaft direction be as small as possible so as to reduce the size and the weight of the whole nacelle.